The subject matter disclosed herein relates generally to the field of elevator systems, and specifically to a method and apparatus for bringing an elevator to a controlled stop when power from an external power source is unavailable.
A typical elevator system includes a car and a counterweight disposed within a hoistway, a plurality of tension ropes that interconnect the car and counterweight, and a drive unit having a drive sheave engaged with the tension ropes to drive the car and the counterweight. The ropes, and thereby the car and counterweight, are driven by rotating the drive sheave. Traditionally, the drive unit and its associated equipment were housed in a separate machine room.
Newer elevator systems have eliminated the need for a separate machine room by mounting the drive unit in the hoistway. These elevator systems are referred to as machine room-less systems. Traditionally elevator systems have been dependent on an external power source for operation, which complicates operation in the event external power source is unavailable.